test: ensure reason is checked for invalid blocks rejection

test/functional/feature_block.py

@@ -161,6 +161,8 @@ class FullBlockTest(BitcoinTestFramework):
             if template.valid_in_block:
                 continue
 
+            assert template.block_reject_reason or template.reject_reason
+
             self.log.info(f"Reject block with invalid tx: {TxTemplate.__name__}")
             blockname = f"for_invalid.{TxTemplate.__name__}"
             self.next_block(blockname)